Circuits and Methods for Providing an Impedance Adjustment

ABSTRACT

An apparatus includes a signal generator and a control circuit. The signal generator includes a control terminal and includes a current electrode coupled to a terminal that is configured to couple to a power line to receive direct current (DC) power from a power generator. The control circuit is coupled to the current electrode and the control terminal of the signal generator. The control circuit determines an impedance associated with the power generator and applies a control signal to the control terminal of the signal generator to produce an impedance adjustment signal on the current electrode for communication to the power generator through the power line in response determining the impedance.

FIELD

The present disclosure is generally related to power generation systems,and more particularly to systems for remote detection and adjustment ofimpedances within a power generation system.

BACKGROUND

Power generators convert mechanical energy or solar energy into directcurrent (DC) power, which can be transmitted through a power line to apower inverter that converts the DC power into an alternating current(AC) power. Efficient power transmission between each power generatorand the power inverter requires impedance matching. Unfortunately, theperformance of a particular power generator may vary during operation.For example, clouds may cast shadows on solar panels, causing asignificant drop off in power generation from the particular solarpanel. In another example, wind speeds may vary, causing the powerproduction of a particular wind turbine to vary. With such variations,the internal impedance of the environmental transducer may also vary.

SUMMARY

In an embodiment, apparatus includes a signal generator and a controlcircuit. The signal generator includes a control terminal and includes acurrent electrode coupled to a terminal that is configured to couple toa power line to receive direct current (DC) power from a powergenerator. The control circuit is coupled to the current electrode andthe control terminal of the signal generator. The control circuitdetermines an impedance associated with the power generator and appliesa control signal to the control terminal of the signal generator toproduce an impedance adjustment signal on the current electrode forcommunication to the power generator through the power line in responsedetermining the impedance.

In another embodiment, a circuit for use in power control systemsincludes a plurality of inputs configured to couple to a respectiveplurality of power generators through associated power lines andincludes a plurality of signal generators. Each of the plurality ofsignal generators has a control terminal and has a current electrodecoupled to a respective one of the plurality of inputs. The circuitfurther includes a plurality of detectors and a controller. Each of theplurality of detectors includes an input coupled to one of the pluralityof inputs and an output. The controller is coupled to the output of eachof the plurality of detectors and to the control terminal of each of theplurality of signal generators. The controller receives a signal fromone of the plurality of detectors indicating an electrical parameterassociated with a selected one of the plurality of inputs. Thecontroller selectively controls one of the plurality signal generatorscoupled to the selected one of the plurality of inputs to communicate animpedance adjustment signal to a power generator of the respectiveplurality of power generators coupled to the selected one of theplurality of inputs.

In still another embodiment, a method includes controlling a signalsource during a first mode to selectively apply a signal to an inputterminal configurable to couple to a power line for receiving a powersupply and measuring an electrical parameter of the input terminalduring the first mode. The method further includes determining animpedance associated with the power line in response to measuring theelectrical parameter and controlling the signal source during a secondmode to provide an impedance adjustment signal to the input terminal forcommunication to a remote device through the power line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial block and partial circuit diagram of an embodimentof a system including a power inverter having a control circuit forcontrolling an impedance adjustment in a remote power generator.

FIG. 2 is a block diagram of an embodiment of a method of controlling aswitched impedance to determine the impedance of the power generator andto communicate an impedance adjustment to the power generator.

FIG. 3 is a block diagram of the system of FIG. 1 including an expandedview of an embodiment of the remote power generator.

FIG. 4 is a flowchart of an embodiment of a method of producing a set ofcontrol parameters based on powers received from each power generatorsand their line impedance.

FIG. 5 is a flow diagram of an embodiment of a method of receiving acontrol signal at a power generator and applying an impedance adjustmentaccording to the control signal.

FIG. 6 is a flowchart of an embodiment of a method of receiving acontrol signal at a power generator and applying an impedance adjustmentaccording to the control signal.

In the following description, the use of the same reference numerals indifferent drawings indicates similar or identical items.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of systems, circuits, and methods are described below thatcan be used to manage impedance matching between remote devices (such asenvironmental power generators) and a central power inverter. Inparticular, a central inverter includes a controller that uses aswitched impedance or another signal source to apply a signal to aninput terminal configurable to couple to a power line for receiving apower from a remote device. The controller receives one or moremeasurements associated with an electrical parameter of the inputterminal before and after application of the signal. The controllerinfers an impedance associated with the power line in response to theone or more measurements. Further, the controller is configured tocontrol the switched impedance or other signal source to apply atime-varying signal to the input terminal to provide an impedanceadjustment signal to the remote device through the power line. Thus, thesame circuit and the same power line can be used to receive power and tocommunicate impedance information to the remote device, which impedanceinformation can be used to provide impedance matching to enhance theefficiency of the power delivery.

FIG. 1 is a block diagram of an embodiment of a system 100 including apower inverter 102 having a controller 108 for controlling an impedanceadjustment in a remote power generator. Power inverter 102 is coupled toa plurality of power generators, such as environmental power generators104 and 106. In an example, environmental power generators 104 and 106can be environmental transducers configured to convert energy from anenvironmental energy source (such as the sun, wind, water, etc.) intoelectricity. Such environmental transducers can include solar panels,wind turbines, water turbines, or other transducers to convert kineticenergy from the environment into electricity. Environmental powergenerators 104 and 106 produce electricity from the kinetic energy ofthe environment and provide the electricity to power inverter 102.

Environmental power generator 104 includes an internal impedance 130,which is coupled to input node 110 and which may vary according toenvironmental conditions. Environmental power generator 104 furtherincludes a variable impedance 132, which is coupled to input node 110and which can be controlled to adjust the impedance of Environmentalpower generator 104.

Power inverter 102 includes a first input node 110 coupled toEnvironmental power generator 104 and a second input node 120 coupled toEnvironmental power generator 106. Power inverter 102 further includes acontroller 108 (such as a processor), which controls operation of thepower inverter 102. Further, power inverter 102 includes a detector 116including an input coupled to input node 110 and an output coupled tocontroller 108. Controller 108 includes an output coupled to an input ofa signal source 111, which has an output coupled to input node 110.Power inverter 102 also includes a detector 126 including an inputcoupled to input node 120 and an output coupled to controller 108. Asignal source 128 includes an input coupled to an output of controller108 and an output coupled to input node 120.

Environmental power generators can exhibit variability in terms of theirpower output as well as variability in their internal impedance, whichmay result in efficiency reduction due to impedance mismatches betweenthe environmental power generator, the DC power line, and the powerinverter on the other end of the DC power line. In an example, due toinherent performance inconsistency among solar panels caused bynon-uniformity of solar cells and their varying rates of degradation,variable shading from buildings, trees or shifting clouds, and the likeeach solar panel's impedance may vary over time. Similarly, for windturbines, inherent performance inconsistency among wind turbines andvariability in wind speeds and direction can produce impedancevariations. Some variations (such as degradation or non-uniformity) mayvary from unit to unit but may remain relatively constant over time. Incontrast, some variations, such as those due to rapidly changing factors(such as the weather) may result significant losses in efficiency unlessthe impedance can be adjusted. In some instances, it may be desirable toadjust the impedance dynamically, periodically, such as every a fewseconds, to reflect the varying conditions and performances of the oneor more DC power generators.

In a particular embodiment, any number of environmental power generatorscan be deployed in a power generation system, such as a solar farm. Eachenvironmental power generator 104, 106 and others (not shown) convertskinetic energy into electricity and outputs DC power to a centralinverter, such as power inverter 102, which collects the DC power fromthe various environmental power generators, converts the DC power intoAC power synchronized to the power grid, and outputs the AC power to autility power line.

As mentioned above, the internal impedances 130 and 140 of environmentalpower generators 104 and 106 can vary due to variable environmentalconditions. Each of the environmental power generators 104 and 106includes a variable impedance 132, 142, etc., which can be dynamicallyand individually adjusted by controller 108 to substantially match theimpedances to enhance the overall energy flow from environmental powergenerators 104 and 106 into power inverter 102.

In an example, controller 108 uses detectors 116 and 126 to measure anelectrical parameter (such as a voltage level, a current level, acomplex impedance, etc.) before and after applying a signal to outputinput node 110 and/or 120. In an example, controller 108 measures theelectrical parameter, and then controls signal source 111 to selectivelyapply a signal to input node 110 and measures the electrical parameteragain. In a particular example, signal source 111 applies a relativelylow voltage to input node 110. In a particular example, signal source111 can include a transistor having its drain coupled to input node 110,its source coupled to a first terminal of a resistor that has a secondterminal coupled to a power supply terminal (e.g., ground), and acontrol terminal coupled to controller 108. In this instance, controller108 activates the transistor to provide a current flow path from inputnode 110 to ground across the resistor. By controlling the transistor toallow current flow through the resistor to ground, controller 108controls the signal source 111 to apply a signal to input node 110 or toalter the impedance at input node 110.

In response to the signal or impedance applied to input node 110,detector 116 detects an electrical parameter associated with input node110. The electrical parameter can include a current level, a voltagelevel, a time-varying signal (such as an exponentially decaying signal),or another electrical parameter. Detector 116 provides a signal relatedto the detected electrical parameter to controller 108 each time ameasurement is captured. In an example, detector 116 can include ananalog-to-digital converter (ADC) and/or a resistor for sampling ananalog current or voltage level at input node 110 and to provide digitaloutputs to controller 108 that represent the electrical parameter.Detector 116 can be activated periodically or can be continuously activefor sampling the electrical parameter at input node 110.

In response to receiving one or more samples, controller 108 determinesan impedance associated with environmental power generator 104. Theimpedance may be inferred from samples captured by detector 116 beforeand after application of a signal by signal source 111. In one example,the samples can be used to determine an impedance associated with theenvironmental power generator 104. In response to determining theimpedance, controller 108 selectively controls signal source 111 toprovide one or more signal pulses to input node 110 to communicate animpedance adjustment to environmental power generator 104. Inparticular, while power inverter 102 is receiving DC power from theenvironmental generator, signal source 111 can apply a signal to the DCpower line, which signal is detectable at any point along the DC powerline, including at the environmental power generator 104.

In response to the one or more signal pulses at input node 110, acontroller within environmental power generator 104 can adjust variableimpedance 132, improving the overall efficiency of the system 100. Whilevariable impedance 132 is depicted as being in parallel with internalimpedance 130 (which may be a fixed impedance), variable impedance 132may be in series with internal impedance 130.

In an example, power inverter 102 is configured to detect the impedanceof each of the environmental power generators to which it is coupled,including environmental power generators 104 and 106, and to selectivelyand independently adjust the variable impedances of the environmentalpower generators as needed. In contrast to impedance calibrationprocesses that require all of the power and impedance measurements to betaken at each power generator and transmitted to a central inverter,power inverter 102 uses signal sources 111 and 128 to provide a remotemeasurement method to allow the measurements can be carried out at thecentral inverter (i.e., at the power inverter 102). Power inverter 102uses the measured data to determine an impedance value of each of theenvironmental power generators and to selectively signal each of theenvironmental power generators to adjust their internal impedances toachieve a desired overall system power output. By adjusting theimpedance, an impedance match can be achieved between the power inverter102 and each environmental power generator 104 and 106 to provide adesired efficiency.

Detectors 116 and 126 and signals sources 111 and 128 make it possibleto capture an impedance measurement on live power line and tocommunicate impedance adjustments and other information through the livepower line. Signal sources 111 and 128 make both functions possible. Insome instances, the signal sources 111 and 128 may be implemented as aswitched impedance (or switchable resistance as shown in FIG. 2), whichcan be used both to capture the impedance measurement and to sendimpedance adjustments to the environmental power generators 104 and 106.One possible example of a signal source, such as signal sources 111 and128 are described below with respect to FIG. 2.

FIG. 2 is a circuit diagram of an embodiment 200 of signal source 111,which can be used in the power inverter of FIG. 1, for providing animpedance adjustment. Signal source 111 includes a transistor 206 havinga first current electrode 204 coupled to output node 110 for providingan output, a control terminal 202 for receiving a bias signal and/or acontrol signal from a controller (such as a digital signal processor(DSP) 108 in FIG. 1, a microcontroller unit, or other control circuit),and a second current electrode coupled to a first terminal of a resistor208, which has a second terminal coupled to ground.

In this illustrated example, transistor 206 is a metal oxidesemiconductor field effect transistor (MOSFET) coupled in series with aload resistor (resistor 208) to provide an extra load to the in-comingDC power supply at output node 110. When the transistor 206 is turned onfor a short period of time (such as a few micro-seconds) by applying acontrol signal to control terminal 202, transistor 206 couples resistor208 to output node 110, changing the input impedance. By measuring thevoltage and/or current at output node 110 before and after the impedanceis changed, the difference between the before and after measurements canbe used by DSP 108 to determine the DC line impedance.

Further, DSP 108 can apply control signals to control terminal 202 fordata communications as well. If transistor 208 is an n-channel MOSFET,each time a logic high signal is applied to control terminal 202,transistor 206 couples resistor 208 to output node 110, causing a dip orabrupt change in the DC power level at output node 110 and on the DCpower line coupled to output node 110. This dip or abrupt change can bedetected everywhere on the DC power line, including at the environmentalpower generator. Similarly, each time a logic low (or zero) signal isapplied to control terminal 202, resistor 208 is disconnected fromoutput node 110 and the DC power level returns to its steady statelevel. By selectively coupling resistor 208 to output node 110, a signalcomprising ones and zeros can be transmitted through the live powercarrying line to the environmental power generator 104. Such ones andzeros can be used to communicate impedance adjustments through the livepower line to the environmental power generator 104. In an example, acontroller, such as DSP 108, can modulate the control signal applied tocontrol terminal 202 to control timing of transitions in the impedanceadjustment signal applied to output node 110 to shape a power spectrum.In some instances, such power spectrum shaping may be utilized to reduceradiation of electromagnetic interference that might cause interferencewith nearby receivers.

The same detection and signaling technique may be used to detect DCpower line impedances of each power line and to remotely controladjustable impedances of multiple environmental generators. For example,when used in conjunction with a solar array, power inverter 102 maydetect a line impedance of each DC power line and selectively adjustimpedances at each solar panel in the array. In particular, detector 110measures an electrical parameter at output node 110. Controller 108applies a control signal to control terminal 202 to allow current flowthrough transistor 206 (applying a first signal to output node 110). Inresponse to application of the control signal, detector 116 measures theelectrical parameter again. Controller 108 determines an impedance of apower line coupled to output node 110 based at least in part on thefirst and second measurements.

In some instances, controller 108 may determine the impedance based on aplurality of measurement of the electrical parameter captured over aperiod of time. In response to detecting the impedance, controller 108can control transistor 206 to selectively couple resistor 208 to outputnode 110, communicating the measurement results from power inverter 102to any environmental generator coupled by DC power line to output node110. In particular, by applying pulses to control terminal 202,controller 108 causes transistor 206 to produce related changes to theelectrical parameter at output node 110, which can be detected by anydevice coupled to the DC power lines. This provides a low-cost way tocommunicate impedance information and/or impedance adjustment signals toone or more attached environmental power generators, such asenvironmental power generator 104. A representative example of onepossible embodiment of an environmental power generator is describedbelow with respect to FIG. 3.

FIG. 3 is a block diagram of a system 300 including an expanded view ofan embodiment of the remote power generator 104 of FIG. 1. System 300includes power inverter 102 coupled to environmental power generator 104by a DC power line. Power inverter 102 includes controller 108, signalsource 111 and other components described above with respect to FIGS. 1and 2.

Environmental power generator 104 includes a power transducer 302, suchas at least one solar panel, a wind turbine, a water turbine, or someother component that converts environmental or kinetic energy intoelectricity. Power transducer 302 includes an output coupled to a DCpower line 303, which has a line impedance (represented by a block 304labeled “Line Impedance”). Environmental power generator 104 furtherincludes a detector 306 including an input coupled to the DC power line303 and an output coupled to an input of a microprocessor 308.Microprocessor 308 includes an output coupled to an input of a variableimpedance 310, which has an output coupled to DC power line 303. Whilevariable impedance 310 is depicted as being in parallel with lineimpedance 304, in some embodiments, variable impedance 310 may include avariable resistance, a switchable resistive network, a variablecapacitor, a switched capacitive network, other linear or non-linearimpedances, or any combination thereof.

In an example, power transducer 302 produces DC power from environmentalenergy and provides the DC power to DC power line 303. As previouslydiscussed, controller 108 within power inverter 102 determines a lineimpedance associated with DC power line 303 and environmental powergenerator 302 and controls signal source 111 to apply an impedanceadjustment signal to DC power line 303. The impedance adjustment signalmay include a sequence of logical ones and zeros or a sequence of pulseshaving modulated pulse widths.

Detector 306 within environmental power generator 104 detects theimpedance adjustment signal and provides data related to the impedanceadjustment signal to microprocessor 308. In response to the data,microprocessor 308 selectively controls variable impedance 310 to applya desired impedance to DC power line 303. In a particular example, thevariable impedance 310 can be adjusted periodically and/or as needed toenhance the efficiency of the DC power supply from environmental powergenerator 104.

In some instances, the impedance adjustment signal may be impedancemeasurement data, which can be used by microprocessor 308 to determinean adjustment for variable impedance 310. Alternatively, the impedanceadjustment signal may include adjustment data, which can be applied bymicroprocessor 308 to adjust variable impedance 310.

FIG. 4 is a flow diagram of an embodiment of a method 400 of providingan impedance adjustment. At 402, a DC power supply is received from apower generator through a power line coupled to an input of a circuit.In an example, the power generator can be an environmental powergenerator (such as a solar panel system, a windmill power system, awater-based power generator. Further, the circuit can be included withina power inverter of a power generation system having one or more powergenerators.

Advancing to 404, a controller of the circuit controls a signal sourceduring a first mode to apply a signal to the input. The signal sourcecan include a switched resistance that can be selectively coupled to theinput to adjust the effective line impedance. Alternatively, the signalsource can be a line driver or other circuit configured to apply atime-varying signal to the input. Continuing to 406, the controllerdetermines an impedance associated with the power generator based on anelectrical parameter of the input during the first mode. In an example,the controller measures an electrical parameter before and during thefirst mode and the impedance is determined as a function of the changein the electrical parameter before and during application of the signalto the input.

Proceeding to 408, the controller controls the signal source during asecond mode to communicate an impedance adjustment to the powergenerator through the power line in response to determining theimpedance. In an example, controller controls the signal source to applyone or more signals to the power line to communicate data, commands,instructions, or any combination thereof to a microprocessor of thepower generator.

As previously discussed, by selectively altering an impedance at theinput of the circuit, a value of the electrical parameter of the inputis varied, which variation is detectable by any device coupled to thepower line. Another example of a method of providing an impedanceadjustment is described below with respect to FIG. 5.

FIG. 5 is a flow diagram of an embodiment of a method 500 of providingan impedance adjustment. At 502, DC power is received from multiplepower generators through power lines at inputs of a circuit, such as apower inverter. Advancing to 504, line impedances of each powergenerator are measured. In an example, controller 108 controls signalsources, such as signals sources 111 and 128 to apply signals to nodes110 and 120 (i.e., inputs coupled to power generators 104 and 106 inFIG. 1). Controller 108 then uses detectors 116 and 126 to detect theline impedances. In a particular example, controller 108 applies thesignal by selectively activating a switch (such as transistor 206 inFIG. 2) to couple a resistor (such as resistor 208) to the input (node110).

Proceeding to 506, the controller determines electrical parameters foreach of the generators to improve a power output parameter. In anexample, the electrical parameter is determined using a detector of thecircuit. In one instance, the controller determines an optimalelectrical parameter for each of the generators to achieve a maximumpower output of the whole system. Moving to 508, the controller infersan ideal line impedance for each power generator in response todetermining the electrical parameters. The ideal line impedance may beinferred from a change in the electrical parameter before and afterapplication of the signal to the input. The controller may determine animpedance match based on the line impedance.

Continuing to 510, the controller determines an adjustment for avariable impedance of each power generator in response to inferring theimpedances. Advancing to 512, the controller selectively transmits theimpedance adjustment to each power generator independently using asequence of pulses to produce a control signal for each of the powergenerators to adjust its impedance. In an example, if no adjustment isneeded based on the impedance, the controller does not send an impedanceadjustment signal to that particular power generator while sendingimpedance adjustment signals to other power generators. Further, eachimpedance adjustment can be unique relative to other impedanceadjustments. In a particular example, the impedance adjustment signaltransmitted to any of the power generators includes a sequence of pulsesrepresenting a control signal, which sequence is detectable by the powergenerator and which can be decoded by the power generator to determineand apply the adjustment to adjust the variable impedance at the powergenerator.

In an embodiment, prior to measuring the line impedance (block 504), themethod 500 may include applying a signal to the input node, such as byselectively coupling a resistance to the input node via a transistor. Inthis instance, the controller infers the line impedance based on achange in the electrical parameter before and after coupling theresistance to the node. Further, in some instances, block 510 may beomitted, and the measurement data can be communicated by coupling theresistance to the input (selectively) to affect the DC voltage level onthe input node, which changes in the DC voltage level can representencoded signals for communicating the measurement data to the powergenerator. In an embodiment, the control signal may be pulse widthmodulated or may include a sequence of ones and zeros that providesufficient data to adjust the impedance at the power generator.

While the methods 400 and 500 described above with respect to FIGS. 4and 5 have provided examples of methods of providing an impedanceadjustment, the signal applied to the node coupled to the DC power lineis detectable at any point along the DC power line. An example of amethod of adjusting a variable impedance of a power generator coupled tothe DC power line in response to the signal applied to the DC power lineis described below with respect to FIG. 6.

FIG. 6 is a flow diagram of an embodiment of a method 600 of receiving acontrol signal at a power generator and applying an impedance adjustmentaccording to the control signal. At 602, a power generator convertsenvironmental energy (or some other energy source) into DC power.Continuing to 604, the power generator provides the DC power to a powerline. Advancing to 606, a microcontroller of the power generator detectsa sequence of changes in one or more electrical parameters associatedwith the power line. In an example, the micro controller may receive adetection signal from a detector representing the electrical parameter.In a particular example, the sequence of changes can be a time-varyingvoltage, a sequence of pulses, a sequence of current changes, or anothersequence of changes in the electrical parameter.

At 608, the microcontroller of the power generator determines animpedance adjustment in response to the detected sequence of changes inthe one or more electrical parameters. In a particular example, thesequence of changes can include encoded data representing an impedanceadjustment. Proceeding to 610, the microcontroller of the powergenerator applies the impedance adjustment to alter a variable impedanceof the power generator according to the sequence of changes. In anexample, the impedance adjustment alters the variable impedance toachieve an optimal power line impedance for the system to improve theoverall power production.

In conjunction with the systems, methods and circuits described abovewith respect to FIGS. 1-6, a circuit is disclosed that includes an inputterminal configurable to couple to a power line for receiving a powersupply, a signal source coupled to the input terminal, a detectorcoupled to the input terminal, and a controller coupled to the signalsource and to the detector. The controller controls the signal source toapply a first signal to the input terminal and receives measurement datafrom the detector. In response to the measurement data, the controllerinfers an impedance associated with the power line and controls thesignal source to apply a second signal to the input terminal forcommunicating an impedance adjustment to a power generator coupled tothe power line. In some instances, measurements may be captured beforeand after application of a signal. Alternatively, different signals maybe applied and the measurements taken in response thereto.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. An apparatus comprising: a signal generator including a controlterminal and including a current electrode coupled to a terminalconfigured to couple to a power line to receive direct current (DC)power from a power generator; and a control circuit coupled to thecurrent electrode and the control terminal of the signal generator, thecontrol circuit determine an impedance associated with the powergenerator and to apply a control signal to the control terminal of thesignal generator to produce an impedance adjustment signal on thecurrent electrode for communication to the power generator through thepower line in response determining the impedance.
 2. The apparatus ofclaim 1, wherein the control signal controls the signal generator toproduce a sequence of pulses to control a variable impedance of thepower generator.
 3. The apparatus of claim 2, wherein the controlcircuit modulates the control signal to control timing of transitionswithin the impedance adjustment signal to shape a power spectrum at theterminal.
 4. The apparatus of claim 1, wherein the signal generatorcomprises: a transistor including the current electrode, the controlterminal, and a second current electrode; and a resistor including afirst terminal coupled to the second current electrode and a secondterminal coupled to a power supply terminal.
 5. The apparatus of claim1, wherein the control circuit controls a plurality of signal generatorsto provide impedance adjustment signals to a plurality of powergenerators through a respective plurality of terminals.
 6. The apparatusof claim 1, wherein the control circuit: applies a first signal to thecontrol terminal of the signal generator to alter an impedance at theterminal; detects a change in an electrical parameter of a signal on theterminal in response to applying the first signal; determines theimpedance of the power generator in response to detecting the change;and generates the control signal based on the impedance of the powergenerator to produce the impedance adjustment signal.
 7. The apparatusof claim 6, wherein the control signal includes a sequence of pulsesthat toggle the signal generator to produce the impedance adjustmentsignal.
 8. A circuit for use in power control systems, the circuitcomprising: a plurality of inputs configured to couple to a respectiveplurality of power generators through associated power lines; aplurality of signal generators, each of the plurality of signalgenerators including a control terminal and including a currentelectrode coupled to a respective one of the plurality of inputs; aplurality of detectors, each of the plurality of detectors including aninput coupled to one of the plurality of inputs and an output; and acontroller coupled to the output of each of the plurality of detectorsand to the control terminal of each of the plurality of signalgenerators, the controller to receive a signal from one of the pluralityof detectors indicating an electrical parameter associated with aselected one of the plurality of inputs, the controller to selectivelycontrol one of the plurality signal generators coupled to the selectedone of the plurality of inputs to communicate an impedance adjustmentsignal to a power generator of the respective plurality of powergenerators coupled to the selected one of the plurality of inputs. 9.The circuit of claim 8, wherein each of the plurality of signalgenerators comprises a transistor including a first current electrodecoupled to one of the plurality of inputs, a control terminal coupled tothe controller; and a second current electrode resistively coupled to apower supply terminal.
 10. The circuit of claim 8, wherein thecontroller is configured to: apply a bias signal to the control terminalof the one of the plurality of signal generators to alter an impedanceat the selected one of the plurality of inputs; determine electricalparameters associated with the selected one of the plurality of inputswhile receiving direct current (DC) power from the one of the powergenerator; and determine an impedance of the power generator in responseto determining the electrical parameters.
 11. The circuit of claim 10,wherein the controller selects the one of the plurality of signalgenerators to communicate the impedance adjustment signal to the powergenerator in response to inferring the impedance.
 12. The circuit ofclaim 10, wherein the electrical parameters comprise a voltage level atthe selected one of the plurality of inputs.
 13. The circuit of claim10, wherein the electrical parameters comprise a timing of a change in avoltage level at the selected one of the plurality of inputs.
 14. Thecircuit of claim 8, wherein the controller controls the one of theplurality of signal generators to apply a sequence of pulses to theselected one of the plurality of inputs to communicate the impedanceadjustment signal to the power generator.
 15. The circuit of claim 14,wherein the controller controls timing of transitions within thesequence of pulses to shape a power spectrum of the impedance adjustmentsignal at the selected one of the plurality of inputs.
 16. A methodcomprising: controlling a signal source during a first mode toselectively apply a signal to an input terminal configurable to coupleto a power line for receiving a power supply; measuring an electricalparameter of the input terminal during the first mode; determining animpedance associated with the power line in response to measuring theelectrical parameter; and controlling the signal source during a secondmode to provide an impedance adjustment signal to the input terminal forcommunication to a remote device through the power line.
 17. The methodof claim 16, wherein controlling the signal source during the secondmode comprises: determining an impedance adjustment in response toinferring the impedance; and providing a control signal to the signalsource to generate the impedance adjustment signal.
 18. The method ofclaim 16, wherein before controlling the signal source and during thefirst mode and the second mode, the method further comprises: receivinga power supply at the input terminal from the power line.
 19. The methodof claim 16, wherein controlling the signal source comprises applying acontrol signal to a control terminal of a transistor to selectivelycouple a resistor to the input terminal to selectively alter animpedance at the input terminal.
 20. The method of claim 16, whereininferring the impedance comprises: comparing a first measurement of theelectrical parameter taken before the signal is selectively applied tothe input terminal to at least one second measurement of the electricalparameter taken while the signal is being applied to the input terminal;and determining the impedance based on a difference between the firstmeasurement and the at least one second measurement.